Presently mandated requirements for controlling fuel vapor emissions in motor vehicle fuel tank systems require an onboard diagnostic (OBD) test be run periodically during the vehicle service life to determine whether the fuel system is vapor tight or whether fuel vapor is permeating to the atmosphere. Such OBD systems widely employ a sequence whereby a slight vacuum is drawn in the fuel tank and vapor emission control system and the rate of vacuum loss measured to determine whether a prohibitive amount of leakage is present in the system.
Vehicles equipped with such OBD systems have been found to experience widespread problems in service with leakage through the user removable fuel tank filler tube cap. The most common types of problems are improper placement of the fuel filler cap by the user after refueling and failure of the cap seal on the filler tube which is attributable to friction and wear after multiple refueling operations.
In order to provide a fuel tank filler system without the conventional user removable cap, it has been required to provide a fuel vapor tight seal mechanism in the filler tube to prevent fuel vapor emission to the atmosphere upon completion of refueling. Thus, a latchable flapper valve has been proposed and such an arrangement is shown and described in co-pending and commonly-assigned application Ser. No. 11/047,201 filed Jan. 31, 2005 entitled: “Door Latch For Capless Filler Neck”, in the name of Paul D. Walkowski, et al., which describes such a releasable latch mechanism for the flapper door. However, where such a releasable latching mechanism has been proposed for a fuel filler tube flapper valve, it has been desired to provide a permanently installed protective cover which will accommodate the insertion of a refueling nozzle without the need for a user removable cap.
There is a desire for a structure that closes and seals a fuel tank filler tube without requiring a user-removable cap. There is also a desire for a structure that is easy to manufacture and install on the fuel tank filler tube and that is robust and reliable in service and sufficiently compact to fit in the limited space allotted for the filler tube in the vehicle body structure behind the outer fuel filler door.